The Vanquisher of Water - The Power of Princirum, #1

You thought magic would be easy? Kym wanted nothing to do with the magical world since the deaths of her aunt and uncle, but that was before the river attacked her. Now, with her magic discovered, Kym must join a world she never liked or understood. Kym's inability to keep up with her magical training, as well as her resistance to her almost-royal status, makes her an outcast among the Favored. But she doesn't give up, and trains even harder as she competes for Lady Nila's attention.
But the Ruler of Water is a difficult woman to please. Magic and Favored. Rulers and Gods. Festivals and plots. But will Kym choose a side?